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Science Behind Chasing Tornadoes

The tornado of a lifetime snakes down a South Dakota road toward Tim Samaras, an engineer and avid tornado chaser from Denver. Minutes earlier, the storm had destroyed the tiny village of Manchester, fortunately with no loss of life. Samaras and a National Geographic team spent months on the front lines of severe storm research. Their mission was to place weather-measuring probes in the path of a tornado—then get out of the way.

Photograph by Carsten Peter

Written by Priit J. Vesilind

Republished from the pages of National Geographic magazine

Around dinner hour on June 24, 2003, the entire hamlet of Manchester, South Dakota—walls and rooftops, sheds and fences, TVs, refrigerators, and leftover casseroles—lifts from the earth and disappears into a dark, thick, half-mile-wide (0.8-kilometer-wide) tornado. The pieces whirl high in the twister's 200-mile-an-hour (322 kilometer-an-hour) winds, like so much random debris swept clean from the landscape. A mile (1.6 kilometers) or so north of town 36-year-old Rex Geyer pulls the curtains back from the window of an upstairs bedroom and watches Manchester disappear. Rex stands frozen. The tornado seems to be standing still too, not moving one way or the other. It takes him a fearsome minute to realize what that means—that the deadly storm is coming straight for him. Just earlier, Rex had sat down to fried chicken with his wife, Lynette, who is eight months pregnant. "We had heard about some wicked tornadoes down in Woonsocket, where Lynette's from," he would say later. "We were keeping our eyes on the TV, and I was looking outside, and I said, 'Well, geez, it don't really look that bad.'" But now rain is pounding down, obscuring the monster storm bearing down on his two-story farmhouse. Rex's brother Dan, who lives up the road, charges into the house. "He almost rips the screen door off the hinges, and he's hollering, 'We gotta get into the basement!' But I just saw the Manchester debris and don't think we'll survive in the basement, so we pile into Dan's car."

"Should I turn the lights and the TV off?" Lynette asks. She hasn't seen the storm.

"No, no! We have to go now!" They leave everything but a mobile phone.

As they flee, two cars hurtle down a nearby dirt road in the opposite direction—straight at the tornado. Tim Samaras, a 45-year-old electronics engineer from Denver, and his storm-chasing partner, Pat Porter, are in a van that carries six probes, often called "turtles"—squat, 45-pound metal disks that look like flying saucers. Through embedded sensors, the probes can measure a tornado's wind speed and direction, barometric pressure, humidity, and temperature. Samaras's mission, and his passion, is to plant them in the path of the funnel. His hope is that both he and the instruments survive.

Photographer Carsten Peter hangs halfway out the window of the other speeding car, which is driven by veteran storm chaser Gene Rhoden. With them is another kind of probe, a pyramid-shaped aluminum casing loaded with a video and three 35-mm still cameras. Tinman, the team calls it, based on the character from The Wizard of Oz. No one has ever filmed the inside of a tornado—where wind can chew asphalt off a road and drive wooden splinters into tree trunks. Carsten wants to be the first.

The chasers can hear the tornado's jet engine roar and see it snapping power poles as they veer east onto a paved road, past the Geyers' farm and directly into the path of the funnel. Tim skids to a halt to make a drop. "We don't have time! We don't have time!" Pat yells. The monster is plowing up ground only a hundred yards (91.4 meters) away, and the inflow wind is revving up as Tim leaps out just long enough to deposit a probe before scrambling back in. As the chasers speed away, they can see debris roaring in above them: Nails, wire, two-by-fours whip by in winds that will soon reach 200 miles an hour (322 kilometers an hour).

Moments later the cars stop again a short distance down the road. Carsten and Gene haul the 95-pound (43-kilogram) Tinman from their car onto the roadside and activate the cameras while Tim drops another turtle. Two so far. Good, good. But now the tornado is chasing them.

They blast down the road once more, and Tim deploys a third probe. Tinman and two of the three probes take direct hits. The tornado reaches one probe a mere 80 seconds after Tim sets it in place. But suddenly the fury is spent. The tornado changes shape, stretching out long and ropey before rolling limply to the side. And then it simply evaporates.

Tornadoes are among Earth's most violent natural acts. About a thousand of them touch down in the United States each year, more than in any other country in the world. Some are wispy and last only seconds, others rampage across the landscape for more than an hour, but few are as destructive as the one that obliterated Manchester.

By definition tornadoes are rotating columns of air that extend from swelling cumulonimbus clouds to the ground. No one fully understands tornado dynamics, but certain ingredients seem essential to the witches' brew from which twisters emerge: warm, humid air near the ground, colder air aloft, and shearing winds that change direction and speed with height. The most destructive and deadly tornadoes form under the bellies of supercells, large long-lived thunderstorms whose winds are already in rotation. It was a supercell that gave birth to the Manchester tornado.

Forty percent of all U.S. tornadoes occur in the central plains states from March through July, when cool, dry air from the Rocky Mountains clashes with warm, moist undercurrents from the Gulf of Mexico. In such open country you can see entire supercells, some 30 miles (48 kilometers) wide, bulling over the land, spitting rain and hail, their cauliflower tops bursting into the stratosphere. But only one in a thousand thunderstorms becomes a supercell, and only one in five or six supercells spawns a tornado.

Because it's so difficult to measure tornado winds and power, scientists measure tornadoes by the damage they cause. On the Fujita scale, developed by Ted Fujita of the University of Chicago, an F1 storm does moderate damage with hundred-mile-an-hour (160-kilometer-an-hour) winds. An F5 is horrific. The Manchester tornado was an F4.

Today's warning time for tornadoes—the time a family faced with catastrophe has to gather essentials and bolt for the basement or nearest storm shelter—averages 13 minutes. Most warnings rely on the 121 radar stations of the National Weather Service, but conventional weather radar can miss the birth of a tornado in the five to six minutes it takes a unit's single beam to cover its range. Now scientists at the National Severe Storms Laboratory (NSSL) are working to adapt a shipboard system from the U.S. Navy—the Spy-1 phased array radar—for meteorological use. Spy-1 sends out multiple beams in continuous rotation and is five times faster than conventional radar.

For three springs Carsten Peter and I pursue supercells and tornadoes with Tim Samaras, with Anton Seimon, a geographer from Boulder, Colorado, and with some other of America's best storm chasers. We cover more than 50,000 highway miles (80,467 kilometers), lugging Tinman around faithfully. We hit severe weather that rattles our teeth and pits our cars with hailstones. We witness skies of transcendent beauty. And we endure the gypsy life of the storm chaser—truck-stop motels, late-night Subway sandwiches, and dogged resolve. Mostly we tilt at windmills; we see only a few tornadoes. And, as it turns out, we won't really succeed until the last hours of our last day afield.

We base ourselves in Boulder in the foothills of the Rockies, where the Great Plains stretch before us like a giant stage. From here we can reach nearly anywhere on the plains with a day's drive. For the first season, 2001, we hook up with Anton, Tim, and an all-star group of scientists in a six-car chase motorcade. Guiding us are several "nowcasters," meteorologists who continuously monitor weather information and send directions to us on the fly by cell phone.

Our main nowcaster is Erik Rasmussen, a tornado researcher with the University of Oklahoma and one of the brightest stars in severe-storm meteorology. Through numerical computer models, constantly flowing weather maps, and intuition, he can sit at home in his bathrobe and calculate where the best supercell will arrive each day by six o'clock p.m., magic hour for tornado formation. "It's me against the atmosphere," he says. "I try to outguess it."

On May 25 Erik points us to the Texas Panhandle, where conditions look right for spawning a supercell. Our task is to find this incipient monster, if it forms, get just to the southeast of it (the best position for Garsten to get revealing backlight), watch it develop, and ensure we can make a getaway if things get dicey.

When we arrive in Texas, we're not alone. In tornado country, especially since the 1996 motion picture Twister, storm chasing has become a phenomenon. During peak season hundreds of people fan out over Tornado Alley, a belt between South Dakota and Texas. Their vehicles bristle with radio antennas and radar dishes, their dashboards outfitted with computers and satellite-linked televisions.

"Everyone can read the weather maps now," says Stephen Hodanish, a lightning specialist with the National Weather Service whom we meet in a honky-tonk one night. "The information is shared. We don't hide it. So we all know where to go."

Some tornado chasers think of it as a clever computer game come to life. Others become intimate with the atmosphere, the way a trail guide learns to know the woods. Recently, skilled chasers have formed companies that take tourists on "tornado safaris," competing to see who can get clients the best views of the storms. But it's not like going to, say, Niagara Falls, which stays put. Tornadoes are unpredictable, and a wrong decision can be hazardous. I have seen tour buses with windows shattered from hail, the passengers shaken but exhilarated.

Research scientists are out there forecasting and chasing too, of course—teams from meteorological departments at universities and from the NSSL in Oklahoma, where much of today's pioneering work is done. But science of this kind is challenging, for tornadoes resist analysis, and creative computer models can take researchers only so far. "The tornado has become the black hole of meteorology," says Anton. "We really don't know how it works."

To get a better handle on that question, research meteorologists Howard Bluestein, from the University of Oklahoma at Norman, and Joshua Wurman, from the Center for Severe Weather Research in Boulder, join in the hunt each spring. Stationary radar can't see fine detail in distant storms because a radar beam loses focus over long distances, so Wurman's Doppler on Wheels (DOW) radar trucks intercept the storms and study their hidden structure at close range. Bluestein's new mobile Doppler radar has a beam so focused it can detect wind features as fine as 20 to 30 feet (6 to 9 meters) across.

But field programs like these can be counted on one hand, so an extraordinary symbiosis has grown between severe-storm meteorologists and serious-minded amateur storm chasers. "The scientific community likes to crunch numbers," says Lance Bosart, a professor of atmospheric science at the University at Albany, whom I meet at a rest stop in Kansas. "The chase community likes to get there and see things. We want to have readings from as many points as we can, and we need all these people to fill in the blanks."

Amateur chasers may even play a role in an ambitious project planned for the spring of 2007, when dozens of scientists will attempt to surround storms and gather data from every angle.

We reach Texas in time, but Erik's designated storm dissipates into a ragged line of squalls that runs off into the Gulf of Mexico. "We don't chase squall lines," says Anton. "They don't have the vorticity." They don't twist, in other words. We caravan in the Texas Panhandle for days, Merle Haggard on the radio, tooling down the straightest roads in the world, chasing storms that only lease and don't deliver. "HP storms," Tim says disgustedly. "High precipitation pieces of crap." Sleep and nutrition suffer. Sometimes dinner is a bag of corn chips, some beef jerky, and a Coke.

By the middle of June we give it up, leaving 2001 as a good year for those who live in Tornado Alley, but a total bust for us.

The following spring, 2002, we carry our own technology instead of relying on nowcasters. Tim has customized his white Dodge Caravan into an intimidating storm-busters vehicle. A domed television antenna sits on its roof. Screens display Weather Channel broadcasts, global positioning system (GPS) readouts, National Weather Service data, and NOAA satellite images. The van is like a submersible diving into the atmospheric sea.

"A nowcaster is continuously poring through the data," says Tim, "but I'd rather pore through the data myself and then look out the window to see what's developing."

On the early morning of May 23, we're in a cheap motel room in Salina, Kansas, clutching foam coffee cups, pulling weather reports off the Internet. "The Midwest is a chessboard," says Anton. "We stopped play last night, but the atmosphere made several moves overnight, so we tune in to see what they were. And now we have to make our move."

It looks promising. A heavy wind has been unloading on the prairie, twisting the cottonwood leaves onto their pale backsides, leaving grain fields squirming. We head out with the skies overcast, like dirty fleece hanging off an old sheep. Thunderstorms are raging to the south. We haul across the Oklahoma border and reach again into the Texas Panhandle. By 4:40 we're in cattle country, where the towns are rawboned, as if the buildings had been scoured into packing crates by the prairie wind. We pull into Lipscomb, Texas, and a car full of local women rolls up.

"You boys bringin' bad weather here?"

"It's not like we want it for you," I reply.

"Hah. It's not like we're not used to it."

But we're late, and out of position. If we try to drive around the storm, we won't have enough daylight left to see it. So we decide to "punch the core" of the thunderstorm, forcing our way into the "bear's cage," an area between the main updralt and the hail. It's an apt name: Chasing tornadoes is like hunting grizzlies—you want to get close, but not on the same side of the river. Sometimes you get the bear; sometimes the bear gets you.

And so we head straight into the storm and find ourselves splattering mud at 60 miles an hour (97 kilometers an hour) on a two-lane road, threatening to hydroplane, visibility near zero. Anton is less than comforting. "The hail in the bear's cage smashes windows and car tops," he shouts, grinning. "The smaller stuff is kept aloft by the updraft, and only the large chunks fall. It's like small meteorites banging down. Ha-ha-ha!"

When the storm spits us out, we stop to look back at the supercell steaming across the prairie. Its top is shaped like a giant anvil, and lightning flashes from it like artillery. Stacks of cumulonimbus clouds pompadour from its top, and dark wisps of clouds curl like imps from the "wall cloud" that has dropped from its rear flank; that's where tornadoes are known to originate. We sprint into position down a country road and—how does this happen?—pull onto a field full of at least ten other chase cars.

"This storm has the only tornado warning in the nation this evening," Tim explains, "and we're standing in the right place." With all the others. Down the road are the headlights of local spotters, many of them sheriff's deputies. Spotters will react on the side of caution, and account for many false tornado sightings. "Sheriffnadoes," some chasers call these. But spotters' vigilance saves lives and property.

The supercell moves in with an immense, dark, roiling tapestry of clouds that leaves us gaping. Hail roar—hailstones clattering against each other as they fall from high in the storm—resonates like a Harley-Davidson. The storm does not deliver a tornado, but after it passes, lightning scorches the sky for half an hour.

Brad Carter, Tim's chase partner for this trip, shakes his head. "It took me four or five years of driving before I saw my first tornado," he says, "and I've been out here nine years now. If I had seen one right away, on the first trip, maybe I wouldn't have gotten so hooked."

Disappointments arrive daily now. The morning strategy sessions, the long drives, the wild chases across the High Plains, the spectacular busts. It's been two years now without a tornado worth documenting. "We should hire ourselves out as storm-prevention people," says Tim. "Everywhere we go, the storms fizzle out."

The 2003 tornado season is another matter entirely. It starts with an explosive string of May storms that roar through Arkansas, Tennessee, and Missouri, leaving entire towns for dead. But we're still either a step behind or a step ahead. On the way to Colorado, my chase partner, Scott Elder, and I pull into Pierce City, Missouri, where just two weeks before an F3 had flattened homes and left the tidy brick shops and restaurants on the town's main street in rubble.

"We don't have a grocery store left in town," says the police chief, Mike Abramovitz. "It's amazing only one person got killed." That was James Dale Taunton, 51 years old, who had positioned himself in the doorway of the town armory, helping people who sought shelter in the building's basement. Sixty survived there.

Over pancakes one morning, Jon Davies, a veteran meteorologist from Kansas, outlines a paradox, "It's so hard to reconcile the destruction of towns and people suffering," he says, "with something you enjoy doing. You won't see me whooping and hollering under a tornado. These things turn people's lives upside down."

Tornadoes have also ripped the southern plains in the 2003 season, and by the time Carsten, Scott, and I join Tim and Anton for the chase, they have already dropped one probe into a Texas twister. Joshua Wurman's DOW trucks were out on the same storm, so there is complementary data to feed into the computer models. Tim, funded this year by NOAA and a grant from National Geographic's Committee for Research and Exploration, has now successfully deployed four probes in two years. Before his project, in more than ten years of trying, scientists had managed to place such an instrument exactly once: A team from New Mexico Tech made the first successful drop in 1995.

By June 4 we're in a caravan of four cars barreling back down to Texas, where we chase a supercell tagged with a tornado warning into Clayton, New Mexico. On a farm road between fallow cornfields, we find ourselves perpendicular to the storm's inflow wind. Hail hacks at our rooftops. Red-brown soil flows across the road like liquid waves.

And then the world seems to simply disappear. I can see nothing but Tim's red brake lights in front of us. The convoy grinds to a halt as a sandstorm rages, its winds approaching 70 miles an hour (113 kilometers an hour), Tim estimates. Somewhere out there a tornado may be brewing. Tim's van begins to rock. Anton's face turns ashen. We can't see the road, only the tops of telephone poles. Twenty minutes pass. Tim finally radios us: His GPS shows a T intersection in the road ahead that we could reach, and so we roll blindly, foot by foot, out of the sandblaster.

"Some storm," Tim says later. "I don't think I've ever seen anything like it." We head east with dirt still caking our cars, the fenders butting tumbleweeds as big as washing machines. We learn later that there was a tornado somewhere in that storm, but we sure as hell couldn't see it.

Our field time is running out when we caravan into northern Nebraska on June 9. Dew points are looking good there, and the National Weather Service promises a convergence of shearing winds. For the 30th time, this may be the day we finally see a tornado. We head into the undulating dunes of the Sand Hills. The AM radio crackles with static. Turkey towers—tall, thin cumulus clouds that bubble upward—trot along the northwestern horizon.

"I like the shear," Tim says into the walkie-talkie. "There are two updrafts, maybe three, dead ahead of us—actually a bit of an anvil coming eastbound. We'll get off the highway and assess the situation."

Guided by the usual mix of computer images and eyeballing, we zigzag toward the South Dakota border, and by late afternoon we're in storm mode. A dark anvil lowers in the hurly-burly western sky. Hanging beneath it is a wall cloud—like an outboard motor to the vessel of the supercell. Nervous technical jargon flies back and forth: "21Z analysis field shows a 997 millibar low developing southward around Ogallala," Tim radios.

The sky is now rotating majestically, and a confused bird flies into our windshield with a thump, leaving a stain of blood and feathers. And then a triangle of cloud lowers and sharpens into something pointier and leaner. It gathers into a funnel like an elephant's trunk, with the texture of soft gray cotton. It whirls like an apparition, no more than two miles (3.2 kilometers) from us, looking alien in the landscape, as if a spaceship had landed. So, it's happening—after three years of futility. I'm finally going to see a tornado.

The tornado snakes down to the fields, where it's chewing up a maelstrom of soil and vegetation. It seems to stand almost still, and suddenly it's gone! It just lifts up, as if the sky were withdrawing a finger back into its fist.

But we're still racing toward the core of the storm, which will probably spawn more tornadoes. Flashing lights and hee-haw sirens of emergency vehicles roar by. The sky looks heavy enough to sink and crush us when we see another twister bullying across the fields—a squat, malevolent-looking wedge. But it's already past, and we're too late to catch it. We drive to Orchard, Nebraska, the hail still pelting the cars in the approaching darkness.

We're gleeful just to have seen tornadoes, but Anton tosses cold water on the celebration as we heat sandwiches in a gas station microwave. "We had two quality tornadoes that crossed roads, and we were out of position," he lectures. "Had we been three minutes earlier to the first storm, we would have been there for deployment. This was a total project failure."

Most of us won't get another chance. Scott, my chase partner, has already returned home, and now it's time for Anton and me to move on to other projects. But Carsten stays behind with Tim, insisting on a little more time. Over the next two weeks they grow increasingly frustrated. Tornado chasing season is usually over by mid-June. By June 23 they have only one field day left, and Tim is "starting to doubt whether we know what we're doing."

And then the Manchester tornado hits.

When the tornado retreats in that fearful twilight, Tim and Carsten find the countryside obliterated of landmarks. "It's an eerie situation," says Carsten. "First this beautiful, perfect structure coming toward you and this smooth, rushing noise, and then everything is eaten up—everything. Power poles are sucked up out of the ground, all the steel wires are ripped off the metal fences, and the fences are blown down flat, leaving nothing but a pristine meadow. It's really crazy."

Rex Geyer and his family drive through the remains of Manchester with terror in their hearts. They look north. Their tan, two-story farmhouse should be there, set in a grove of trees. Please, please. "But I knew right away," says Rex. "There was nothing left, no trees, no house, no nothing. Just the foundation—picked clean."

Two large, full fuel tanks had been blown into the Geyers' cellar, completely filling the space. Those tanks would have crushed anyone taking refuge from the wind.

Less than an hour before, Tim and Garsten had left three probes and Tinman in the path of the storm. Sobered, they now retrace their steps, hoping to find the instruments intact. "I'd swear we put one of the probes here," Tim says, arriving at a crossroads, "but nothing looks the same."

The air is juicy with the tang of mangled vegetation and evaporating moisture. Among the first on the scene, they check the bleak remains of another missing farmhouse, Harold Yost's home, but no one's there. In Manchester, home to only six people, it seems a miracle that no one died, since they all decided to ride out the storm. One couple survived by crouching in a bathtub. A neighbor was literally sucked through the wall of his trailer home. The building toppled over on him, but the storm quickly whisked it off into the sky, leaving him dazed but alive.

But the turtle probes are there, and the tornado has passed directly over two of them. "It hit one probe and moved north into the cornfield," says Tim. "Then it came back and crossed the road again."

"Amazing! Amazing!" shouts Carsten, leaping around the road.

No one sleeps that night, and as word gets out to the tight-knit chase community, the Internet crackles with congratulations. At first Carsten couldn't find Tinman, but the next day he tracks it 160 yards (146 meters) across the fields, where the wind has tumbled it end over end, leaving a trail of great gashes in the soil. It sits poking out of the mud, its glass portholes smashed, looking like a piece of airline-accident debris. The still cameras fired only a few frames before being destroyed, but those images are probably the closest ever taken of a tornado. Carsten flies out on June 26. In the final hour he has looked deep into the eye of the beast.

Meteorologists respond immediately. Erik Rasmussen casts around on the Internet for other chasers who have photographed or videotaped the Manchester tornado and heads up to South Dakota. Putting tapes together with Tim's measurements from the probes, he may be able to construct a computer visualization of the tornado in action. And examination of Manchester's well-documented demolishment could provide insight into the dynamics of the winds, and how they topple structures.

On July 19 healthy twin girls are born to the Geyers—Hayley and Heather, nicknamed "Twister" and "Stormy" by the local media. Rex struggles with insurance claims and leans on his extended family for help.

The Manchester storm yields some of the most startling measurements ever obtained. One probe registers a drop in barometric pressure of 100 millibars, an astounding measurement that verifies theoretical calculations. Computer models predict that pressure drop is an indicator of wind speed inside the tornado, so this reading will help solve one of the great unknowns: How fast are the winds in the core of a tornado?

"Tim's measurements are some of the best ever made," says Rasmussen. "He's the first to measure everything—temperature, humidity, wind speed and direction of a tornado. The data collected will be a gold mine."